A rape victim is photographed at a clinic in the Democratic Republic of the Congo. Unwatchable draws attention to rape and violence in the DRC. Photograph: Cedric Gerbehaye/MSF

There has been some furore around a new short film, appropriately entitled Unwatchable, in which an English family is attacked by the army. It is shocking because it candidly shows the kind of rape and terror that takes place in the Democratic Republic of the Congo and elsewhere in the world.

The (not very subtle) point is that we wouldn't allow this kind of thing to happen in England. Viewers witness the rape of a teenage girl, the murder of her father and the feeding of his genitals to the mother, all of which happened to a Congolese woman who inspired the script. The graphic nature of the film has caused an outcry among some commentators who think it has gone too far, that the filmmakers are "absolute nutters", and that this "nonsense has got to stop". The Guardian has a piece asking some useful questions, which is worth a read.

The film is horrific, but those who have dismissed it as unacceptable are wrong.

Two things matter in advocacy: truth and effectiveness. In moral terms, speaking the truth is always the right thing to do. I remember a discussion with a friend involved in a political struggle in Colombia, who had lost many loved ones. When I suggested his organisation's plan of action didn't sound like a very good change strategy, he said: "It is not a change strategy, it is a moral stand." Some people have become demoralised by the power of the status quo; they have so lost faith in the possibility of change that simply standing up and telling the truth is what they feel they are called to do.

In campaigning terms, however, there is no point in being right if no one responds in an active way to improve things; the messaging has to be effective as well. Sometimes it can be tempting to prioritise effectiveness over truth. I know of campaigns that have deliberately exaggerated statistics and claims to provoke a reaction. It has sometimes worked, but in the long-term an untruthful strategy may well lose support and legitimacy.

Apart from truth and effectiveness, there may sometimes be ethical considerations regarding the portrayal of people. Some images are both true and effective (such as babies dying of hunger), but their overuse can victimise rather than empower people. If Congolese victims support this film (and from the interview with a rape victim on the film's website, that would appear to be the case), that is a strong argument in its favour.

So let's look at each factor in turn. In terms of truthfulness, does this kind of thing really happen? Yes. But the film has been criticised for drawing a simplistic link between army terrorism and the extraction of minerals required for the manufacture of mobile phones. I don't agree with this assessment. The causes of Congo's wars are many and complex, going far back into history, but can't be fully explained without mentioning the role the trade in minerals has played in deepening conflict.

It may seem harsh to pick on a particular industry (phones). And it is certainly not obvious what the appropriate policy response should be from the international community, since trade restrictions can have perverse effects. But the links made in the film between terror and control of resources are justifiable, and find echoes in many developing countries.

Will the film be effective? The fact that it did not appear to motivate a few highly knowledgeable bloggers does not mean it won't generate a response outside the development policy elite. Shocking people can lead to action. The film induces emotions of pity as well as anger – both powerful forces.

Very few people who watch the film will feel less likely to act in favour of rape victims, but quite a lot will probably be more likely to act because of it. Of course, it will not be for everyone, but it is likely to reach some people who have never before considered the issue.

If the critics are right, and the film proves ineffective, why are they so angry about it? Lots of advocacy is ineffective but does not provoke such strong responses. Some of the film's critics have implied that its images are unacceptable because they make you feel uncomfortable or ill. But the sensitivities of those watching the film are not of particular concern when the issue is so important. It strikes me that some would simply prefer the realities of war not to be brought home to a western public living relaxed lives on a seemingly different planet. I think they should be – we should be reminded of what is happening in other parts of the world, to shake us from our daily routine, and to galvanise us into response.

One of the most shocking images in the film is of the father with blood where his genitals had been. A few years ago, on a march in Colombia against forced displacement, I saw a blown-up photo of a teenage boy who had suffered the same fate. It was held up by his family members, demanding justice. It was a terrible image, but it will stay with me. It makes me angry, and it motivates me to act.

• Please be aware that the film in the following link to the Unwatchable campaign website contains highly graphic scenes of sexual violence: http://www.unwatchable.cc